Answer: She ordered 4 toppings.
Explanation:
Given: Total cost of pizza = $ 12.90
Cost of pizza =$7.50
Price per topping = $1.35
Let x = Number of toppings,
Total cost of pizza = (Cost of pizza) + (price per topping) × (Number of topping)
![12.90= 7.50+1.35x\\\\\Rightarrow\ 1.35x=12.90-7.50\\\\\Rightarrow\ 1.35x=5.4\\\\\Rightarrow\ x=(5.4)/(1.35)\\\\\Rightarrow\ x=(540)/(135)=4](https://img.qammunity.org/2022/formulas/mathematics/high-school/mf0jsdqujxyfosyno1o77nhqfhx8exarn6.png)
hence, she ordered 4 toppings.